When acquiring fingerprints of a subject, it is important that the sequence of the fingerprints are determined and checked to be correct in order to enable accurate searches and comparisons in an AFIS or other fingerprint database at a future date. For this reason, back when fingerprints were taken with ink on paper, the FBI created a Type-14 record where a subject rolls each of his 10 fingers, but also gives a flat impression of his 4 left fingers, his 4 right fingers, and then gives the flats of his two thumbs simultaneously, see FIG. 1 for example. In this manner, one can manually compare the fingerprints of the rolls with those of the flats to determine whether or not by accident or on purpose one or more fingers were rolled incorrectly—for example a left middle finger was rolled when a left ring finger or a right middle finger was required.
In present day, fingerprint capture is performed predominantly by optical means in a scanner and the same methodology that was applied to a Type-14 paper card is applied through the use of an FBI Appendix F certified optical scanner with a 3.0″×3.2″ capture area. The optical scanner is capable of recording the fingerprints of a four-finger slap (and 2-thumb slap) in additional to the rolled fingerprint of each individual finger. Software in the scanner then compares the flats to the rolls in order to determine that the sequence of rolled fingerprint images was correct.
For certain applications, in particular mobile applications where the size and the weight of the fingerprint scanner may be critical, a 2-finger scanner may be preferential over a 4-finger scanner, since a 2-finger scanner is more portable being smaller in size and lower in weight than a 4-finger scanner. This is in sharp contrast to criminal bookings or background checks where the acquisition of 4-finger slaps as part of completing a Type-14 record has always been the standard.
Such a two-finger scanner has a housing with a platen surface (sized for imaging at most two fingers at a time) and optics in the housing directed to the platen for capturing images. As a result, 2-finger scanners cannot, unlike a 4-finger scanners which have a much larger platen and thus larger optics for image capture, simultaneously image all fingers (except thumb) of a subject's hand to provide a flat fingerprint image for typical comparison with individual fingerprints to determine that fingerprint images are each of the correct finger. Thus, it would be desirable to provide a two-finger scanner that assures a subject has properly presented fingers to the scanner's platen in images captured thereof for individual fingerprints as prompted to by the scanner or operator when completing the equivalent of a Type-14 record, even though a rolled finger print image of the hand cannot be performed due to the scanner platen's limited size